Cleaning the gas-swept heating surfaces of heat exchangers



Dec. 16, 1958 B. o. BROMAN CLEANING THE GAS-SWEPT HEATING SURFACES OF HEAT EXCHANGERS Filed April 30, 1954 2 Sheets-Sheet l E: E E: E: z: E: ELW? Dec. 16, 1958 B. o. BROMAN 2,864,587

CLEANING THE GAS-SWEPT HEATING SURFACES OF HEAT EXCHANGERS Filed April 30, 1954 2 Sheets-Sheet 2 United States Patent CLEANING THE GAS-SWEPT HEATING SURFACES 1 OF HEAT EXCHANGERS Bror Olof Broman, Stora Essingen, Sweden, assignor to Aktiebolaget A. Ekstroms Maskinaflar, Stockholm, Sweden Application April 30, 1954, Serial No. 426,797

Claims priority, application Sweden May 15, 1953 6 Claims. (Cl. 257-1) When cleaning the gas-swept heating surfaces of heat exchangers by means of so-called pellet cleaning, as ex emplified in my prior Patents No. 2,665,118 and No. 2,665,119 dated January 5, 1954 in which cleaning particles, usually steel shot, fall onto the heating surfaces, the cleaning particles pass through the heat exchanger and subject the heating surfaces to impact to dislodge material therefrom. The gas flowing through the heat exchanger has its direction of flow and velocity increased and is discharged through a side outlet while the shot pellets are collected in a pocket at the bottom of the heat exchanger and below the gas outlet for return to source for a new cycle through the heat exchanger. This operation is effected in such a way that the particles of dust accompanying the gases through the heat exchanger and the deposits removed from the heating surfaces accompany the flue gases out of the heat exchanger, by suitably altering the speed and the direction of flow of the flue gases in advance of their exit. Thus, the greater portion ofthe dust will, at an early stage, be separated from the cleaning particles, the latter then being conveyed back for use in a new cleaning cycle. Agglomerates of dust particles are collected in a particular and independent separator associated with the pellet outlet, which lets the steel shot pass through, and from which the separated dust particles are removed at intervals.

However, when burning fuel which is rich in ashes, the amount of dust in the flue gases may be so great that a greater or smaller part of the dust, in spite of the measures described above, are separated from the flow of gas together with the steel shot and fall onto the bottom ofthe heat exchanger, from where it accompanies the steel shot in its new cycle, loading'the ducts and the cyclone device or the like in which the cleaning particles are separated from the means of transportation, after which they are again introduced into the heat exchanger. The accumulation of dust at the bottom of the heat exchanger may also cause stagnation in the bottom outlet of said heat exchanger, the circulation of the steel shot being thereby disarranged.

To a certain extent, it is possible by this invention to eliminate these disadvantages by letting outer air through the bottom of the heat exchanger. Owing to the subpressure prevailing in the heat exchanger a rising current of air then will meet the particles of ashes and dust, which therebywill not so easily fall onto the bottom of the heat exchanger. This, however, depends on the magnitude of the subpressure in the heat exchanger which varies with the charge. If the subpressure is very small, the speed of the current of air can be so low, that the dust is not blown back.

In certain cases, for instance in the chemical industry, the gases may be explosive, for which reason air must not be let in. In other cases the gas may be valuable, for example, sulphur dioxide from pyrite furnaces, in which a.dilution with air would be adisadvantage, partly per se and partly due to the fact that the amount of gas Patented Dec. 16,1958

increased by the introduction of air encumbers a possible electrofilter.

.The. present invention is directed to a heat interchange apparatus of the type including a wall means defining a casing having an upper gas inlet and a lower gas outlet and in which heat exchange surfaces are arranged within the casing so that gas, such as flue gases or other hot gases mentioned previously, pass through the apparatus in heat exchange relation with the surfaces, with means being provided to introduce surface cleaning shot pellets within the casing above the surfaces so that these pellets cascade through the casing and ricochet and impact against the surfaces to remove dust and deposits therefrom.

The primary object of the invention is to provide means whereby a portion of the gases flowing out of the apparatus is introduced back into the bottom of the apparatus for not only increasing the flow velocity of the gas leaving the outlet, but also for separating dust, deposits and any other material accompanying the shot pellets so as to carry such deposits, dust or ashes out of the heat exchanger through the gas outlet.

More particularly, the invention has for an object to provide a pellet collecting pocket below the gas outlet, conduit means communicating with and constituting an extension of the gas outlet, a bypass conduit means including an inlet communicating with said conduit means downstream of the gas outlet, and an outlet from the bypass conduit means communicating with the pocket, whereby aportion of the gas flowing through the outlet can pass through the by-pass conduit means for introduction into the pocket to flow upwardly therethrou gh counter-current to. the descending flow of pellets and any material or ash or dust accompanying the same, wherebythe ascending introduced portion of the gas separates such material and ash and dust from the pellets and conveys the separated material. into the gas stream leaving the gas outlet.

.means and the outlet of the by-pass conduit so that the gas can be introduced into the pocket in varying quantities and under varying pressures.

.It is a still more specific object to provide the pellet collecting pocket with screening means that extend downwardly from one wall of the pocket toward the opposite wall and terminate in closely spaced relation thereto to define -a slit so that the introduced medium ascends through the slit while the pellets descend therethrough.

Further and more specific objects will be apparent from the following description taken in connection with the accompanying drawings in which Figure 1 is a longitudinal sectional view partlyin elevation illustrating a heat exchanger-embodying the invention and Figure 2 is a fragmentary view similar to Figure 1 but on an enlarged scale and illustrating the lower portion of the heat ex changer.

In the drawings, Figure 1, the heat exchanger is generally denoted at A and includes tubes B. At the top of the heat exchanger is a collecting device C for receiving cleaning particles, pellets that have been recycled from the bottom of the heat exchanger in a manner as set forth in my prior Patents No. 2,665,118 and No. 2,665,119 dated January 5, 1954. Thus pellets are introduced into the collecting device C by conduit G after being conveyed up to the height of the collecting device C by a conduit means partly indicated at 14in which an air or gas stream is generated by means of a suitable fan not shown. The particles are passed from thecollecting device C through a tube D and impacted against a deflecting member E whereby they are effectively scattered throughout substantially the entire cross sectional area of the heat exchanger and impact and ricochet against the tubes B in their passage through the heat exchanger, this action effectively cleaning the surfaces of the tubes. The flue gases enter the heat exchanger as indicated by arrow F, pass downwards therethrough and transfer heat to the tubes B and then the gases undergo a change in direction of flow as indicated by the arrow H and pass out through the flue gas outlet 15.

In Figures 1 and 2 the numeral designates the lower portion of the heat exchanger which terminates at its bottom in a funnel-shaped pocket 11 serving to collect cleaning particles after they have passed downwardly through the heat exchanger. A duct 12 is connected to the lower end of said pocket, which duct in turn carries at its lower end a separator 13, which serves the purpose of separating greater accumulations of dust and the like. The outlet of the separator opens like an injector into a transportation duct 14 serving the purpose of restoring the cleaning particles to the top of the heat exchanger, from where they are separated in a suitable manner from the air or gas transportation and are again flung over the heating surfaces that is the pellets are introduced into the heat exchanger above the heating sur face therein to cascade through the heat exchanger and impact and ricochet against the surfaces as in my prior patent mentioned above. Directly above the pocket 11 a flue gas outlet 15 is provided in the wall of the heat exchanger for the gas flowing from the heat exchanger.

A conduit means or channel 16 communicates with and constitutes an extension of the flue gas outlet 15 and extends downwardly through the apparatus beneath the pocket 11. Filter means indicated at 17 are provided in this channel 16.

A by-pass conduit means extends in communication between the channel 16 and the pocket 11 and includes an inlet portion or duct 18 communicating with the channel 16 and an outlet portion or duct 20 terminating in communication with the pocket 11. Between the duct portions 18 and 20 is interposed a pump means comprised by a suction fan and a valve means constituted by a choke and shut-off valve 21 is interposed in the duct 20 between the outlet of the fan 19 and the terminal outlet end of duct 20. This structure provides an arrangement in which a portion of the flue gases after they have passed the filter 17 can be diverted from channel 16 to be pressurized by pump 19 and then introduced into the pocket. The valve means 21 is operative to vary the quantity and pressure of the diverted flue gases which are introduced into the pocket. The duct 20 may via branch conduits 22 be connected to corresponding ducts to other heat exchangers, which may be served by the same fan and the same gas channel 16 or may alternatively be in communication with the side of pressure of the flue gas fan of the boiler, a special fan for the device being thereby dispensed with.

In order that the gas supplied through the duct 20 to the bottom of the pocket 11 shall obtain a suitable direction of flow there may be provided in the pocket a screen or baflle 23 inside which the end of duct 20 terminates and a batfle or screen 24 extending at an angle to the screen 23 and lying in front of the outlet end of duct 20, There is a relatively narrow slit 25 formed between the lower terminal edge of said screen 24 and the adjacent wall of the pocket 11. Between the screen 23 which extends from the bottom outlet of the pocket to some distance up the wall of the heat exchanger, and the screen 24 a space is formed into which the gas from the conduit 20 first flows. From there the gas flows through the slit 25 towards the gas outlet 15 where it meets the descending steel shot and dust particles accompanying the steel shot which must pass through the slit in order to penetrate down to the bottom outlet of the pocket. However, the speed of the gas flow is so selected that the dust particles, but not the steel shot, are lifted up toward the gas outlet 15 by the oncoming gas flow from conduit 20, where they are entrained in the gas flow deflected round a deflecting screen baffle 26 extending downwardly and inwardly from the wall opposite the outlet of conduit 20 and are carried out into the gas channel 16. Thereafter the dust particles are caught by the filter 17. The screens may be arranged in such a manner that the width of the slit can be regulated.

By suitably adjusting the dimensions of the slit 25 and the speed of the gas flow through the conduit 20 it is possible to give the rising gas flow the speed required for separating the dust from the steel shot rushing down the walls of the pocket 11. The steel shot, on the other hand, owing to its weight, falls without obstruction through the slit 25 and down into the duct 12 from where it is recirculated.

It is obvious that with a device of the kind described it is possible to guide the course in such a manner that the dust is separated from the steel shot as adequately as possible, and this is carried out with relatively simple means. To blow in gas according to the invention is more advantageous than letting in outer air, which, according to what is stated above causes different inconveniences.

It is to be.understood that the expressions gas or flue gas as utilized in this specification and the accompanying claims, is to be interpreted to be of such scope as to mean not only combustion products, such as those that result from the combustion of a fuel in a boiler, but also any hot gases, the thermal energy of which is to be recovered, as, for example, the sulfur dioxide given off from pyrite furnaces.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

1. In heat interchange apparatus of the type including wall means defining a casing, an upper gas inlet, heat exchange surfaces within the casing, a lower gas outlet below the surfaces and directed laterally of the wall means, means for introducing shot pellets within the casing above the heat exchange surfaces so that for cleaning such surfaces the pellets cascade through the apparatus and ricochet and impact against such surfaces to remove dust and deposits therefrom, a pellet collecting pocket below the gas outlet, conduit means communicating with and constituting an extension of the gas outlet, a by-pass conduit means including an inlet communicating with said first-mentioned conduit means downstream of such gas outlet, and an outlet communicating with said pocket whereby a portion of the gas flowing through the outlet can pass through said by-pass conduit means for introduction into the pocket to flow upwardly therethrough counter-current to the descending flow of pellets and any material, ash or dust accompanying the same whereby the ascending introduced portion of the gas separates material, ash or dust from the pellets and conveys the separated materials into the gas stream leaving the gas outlet.

2. In heat interchange apparatus as claimed in claim 1 and further including pump means interposed in said bypass conduit means and valve means interposed in said by-pass conduit means between the pump means and the outlet of said by-pass conduit means whereby gaseous medium can be introduced into the pocket in varying quantities and under varying pressure.

3. In heat interchange apparatus as claimed in claim 1, and filter means within the conduit means that communicate with and constitute an extension of the gas outlet, said filter means being located between the gas outlet and the inlet of the by-pass conduit means.

4. In heat interchange apparatus of the-type including wall means defining a casing, an upper gas inlet, heat exchange surfaces within the casing, a lower gas outlet below the surfaces and directed laterally of the Wall means, m ans for introducing shot pellets within the casing above the heat exchange surfaces so that for cleaning such surfaces the pellets cascade through the apparatus and ricochet and impact against such surfaces to remove dust and deposits therefrom, a pellet collecting pocket below the gas outlet, means for introducing gaseous medium into the pocket to flow upwardly therethrough countercurrent to the descending flow of pellets and material and ash and dust accompanying the gas flowing through the apparatus, whereby the ascending medium separates material and ash and dust from the pellets and conveys the separated materials into the gas stream leaving the gas outlet, said pocket having downwardly and inwardly inclined wall means and a lower pellet outlet, the means for introducing gaseous medium into the pocket communicating therewith through one wall at a point above the pellet outlet, screening means connected to' said one wall above the point of introduction of medium and extending downwardly and outwardly therefrom toward the opposite wall and terminating in closely spaced relation thereto to define a slit through which pellets descend and introduced medium ascends.

5. In heat interchange apparatus as claimed in claim 4 and in which the size of the slit can be regulated.

6. In heat interchange apparatus of the type including wall means defining a casing, an upper gas inlet, heat exchange surfaces within the casing, a lower gas outlet below the surfaces and directed laterally of the wall means, means for introducing shot pellets within the casing above the heat exchange surfaces so that for cleaning such surfaces the pellets cascade through the apparatus and ricochet and impact against such surfaces to remove dust and deposits therefrom, a pellet collecting pocket below the gas outlet, means for introducing gaseous medium into the pocket to flow upwardly therethrough counter-current to the descending flow of pellets and material and ash and dust accompanying the gas flowing through the apparatus, whereby the ascending medium separates material and ash and dust from the pellets and conveys the separated materials into the gas stream leaving the gas outlet, and the means for introducing medium into the apparatus to flow counter-current to the flow of pellets, material, ash and gas including means defining a restricted passage through which the introduced medium flows upwardly and the pellets and material and ash flow downwardly.

References Cited in the file of this patent UNITED STATES PATENTS 1,400,234 Owens Dec. 13, 1921 1,801,811 Haber Apr. 21, 1931 1,887,722 Schoener Nov. 15, 1932 1,902,719 Payton Mar. 21, 1933 2,048,746 Kidd July 28, 1936 2,096,714 Haldane Oct. 26, 1937 2,236,635 Young Apr. 1, 1941 2,409,442 Montgomery Oct. 15, 1946 2,425,984 Blackman Aug. 19, 1947 2,665,119 Broman Jan. 5, 1954 FOREIGN PATENTS 80,484 Norway July 21, 1952 

